External damping adjustment apparatus and method for suspension system

ABSTRACT

A mechanism and method for externally adjusting the mid-valve stiffness is described and enables adjustment of a mid-valve functionality without disassembly of a suspension system incorporating the invention. The effect of this adjustment on the damping curve is far greater than either low-speed compression adjusters or conventional high-speed compression adjusters. The apparatus combines the valve-stiffening system of a high speed compression adjuster with the sensitivity of the mid-valve. Externally accessible adjustment members are operatively coupled to the mid-valve components located internally in a fork so that manipulation of the adjustment members causes adjustment of the mid-valve and the damping force created by the mid-valve. The apparatus may be utilized in closed cartridge suspension forks (CCSF) and open cartridge suspension forks (OCSF) and other shocks or suspension dampers.

TECHNICAL FIELD

The present invention is in the field of vehicle suspension systems.More specifically, the invention relates to suspension forks or shocksused on motorcycles and bicycles and an externally accessible dampingadjustment system applicable to suspension forks and which allows foradjustment of damping without disassembly of the suspension fork.

BACKGROUND OF THE INVENTION

A suspension system is composed of a spring and a damper. The springsupports the load, and the damper dissipates energy from bumps. Modernsuspension components generate damping, or resistance to movement,through a system of valves that regulate the flow of oil within thedamper. As the suspension compresses and extends, pressure differencesbetween chambers in the damper forces oil to flow through valves fromthe high pressure chamber to the low pressure chamber. The valves arepartially blocked by a stack of flexible steel washers called “shims,”which help maintain the pressure differential, but allow a meteredamount of oil to flow through. As pressure differential builds up acrossthe valve, the outer edge of the shims begin to bend away from the valveface, enabling oil to flow through. Oil flow characteristics aredetermined by the number and shape of ports through the valve bodies,and the stiffness of the shims covering the ports. The greater therestriction to oil flow, the more damping force is generated.

Modern performance suspension dampers can be extremely complex. Theparagraph above describes a simple suspension damper.

Low-Speed Damping Adjusters

Among the many innovations and improvements to suspension components,various external damping adjusters have been developed. External dampingadjustments enable the user to fine-tune the suspension withoutdisassembly. The most common type of damping adjuster is a needle andorifice valve that bypasses the main shim-controlled valve.

These adjusters are often called “clickers” because of the detentmechanism that makes them move in defined increments with a click. Whenthe adjuster is fully closed, the needle shuts off oil flow through theorifice. As the adjuster is opened, the needle backs out the orifice andmore oil can flow through.

Clickers change damping force by about the same amount at all suspensionvelocities. Proportionally speaking, they have a much greater effect onlow speed damping because the total damping force is small at lowspeeds. For example, a two-pound change in damping force created by theadjuster is more significant when total damping force is five poundsrather than fifty pounds. For that reason, clickers are primarilylow-speed damping adjusters. They have no direct effect on the mainvalves.

High Speed Compression Adjusters

A different type of damping adjuster is typically referred to as a “highspeed compression adjuster.” This type is commonly found on shockabsorbers rather that suspension forks, although some models ofsuspension forks use an adaptation of the design.

Rather than regulating the fluid flow bypassing the valve, a high speedadjuster provides a means of externally stiffening a shim stack.Typically, this involves a screw or dial mounted externally on thesuspension that can vary the load on an adjustment spring, which in turntransmits spring force to the shim stack through a pressure plate. Thepressure plate can augment the stiffness of the shim stack according tothe spring force applied by the adjustment spring. The pressure platemay apply pressure to the outermost shim, or to any of the other shimsin the shim stack except for the smallest shim. If it presses againstthe outermost shim, the spring increases the force required to lift theshim edge and open the valve. If the pressure plate presses against anysmaller diameter shim (except for the smallest shim), the spring forcepartially changes to the fulcrum point that the other shims bend around,reducing shim bending leverage and thereby stiffening the shim stack.Regardless of the precise mechanism used to achieve adjustment, theprinciple remains the same.

Because the high speed adjuster stiffens the shim stack, it alters theslope of the damping curve (a plot of suspension velocity vs. dampingforce). This is an important distinction from the vertical shift (y-axisdisplacement) of the damping curve introduced by low-speed adjusters. Inpractice, high speed adjusters usually affect damping force at allsuspension shaft velocities and are not actually confined tohigh-velocity suspension movements.

A common high speed adjuster design incorporates both a high speedadjuster and a low speed adjuster into a single valve. The low speedadjuster needle and orifice is located at the center of the valve, witha high speed spring and pressure plate positioned concentric with thelow speed adjuster screw. In the industry, this is called a dualcompression control adjuster.

High speed adjusters in use today are always located at the base valve,in part because the base valve is physically connected to the damperadjacent to an externally visible portion of the damper housing. Thismakes it a practical and accessible location to locate a complexadjuster mechanism.

Types of Compression Valves

Shock absorbers and many types of suspension forks use two differentvalves to generate compression damping. The nomenclature varies, butherein they will be referred to as the “base valve” and the “mid-valve,”terms which are typical in describing cartridge forks. The base valvecontrols fluid flow that results from the damping rod entering thecartridge during a compression stroke, and displacing fluid from thecartridge. The displaced volume of fluid exits the cartridge through thebase valve. When the fork extends, a check valve on the opposite side ofthe base valve opens and allows fluid to refill the cartridge withminimal resistance. Thus, the base valve functions only as a compressionvalve. It is attached to the end of the cartridge in a fixed positionrelative to externally visible parts of a suspension fork. In unsealed“open cartridge” fork designs, the base valve is located at the bottomof the fork near the axle lug. In sealed “closed cartridge” forkdesigns, the base valve is usually located at the top of the fork.

The mid-valve is attached to the end of the damping rod, deep within thecentral body of the damper. It is not directly connected to any externalportion of the damper housing, but rather is connected to the damperhousing at the opposite end of the damping rod. The mid-valve cyclesback and forth inside the cartridge as the suspension compresses andrebounds. It is a bi-directional valve, meaning it generates dampingforce both when the damper compresses and when it extends (compressionforce as the fork is compressed, and rebound force as the fork extends).To accomplish this, the valve body has two sets of ports and two sets ofshims oriented on opposite sides of the piston face. Unlike the basevalve, fluid flow through the valve does not depend on fluid displacedby the damping rod as it enters the cartridge. It moves “through” thefluid with suspension movement. A larger volume of oil flows through themid-valve compared to the base valve, so other factors being equal, itcan generate more damping force than the base valve.

In traditional configurations, the rebound-side shim stack is fixedsecurely to the piston face, but the mid-valve shim stack is setup with“float”. Float means that during a compression stroke the shims canfreely move a fixed distance away from the piston face before reaching ahard stop, whereupon the shim stack begins to generate a damping force.Float values are often very small, in the range of 0.5 mm, but thatsmall float gap greatly reduces the compression damping force the valvegenerates. With a floating shim stack, the mid-valve can be configuredto produce little or no damping force at low velocities, but highdamping forces at mid- or high-velocity movements.

The floating shim stack technique is common because the mid-valve isextremely sensitive. Since it passes a larger volume of fluid comparedwith the base valve, it has the potential to generate more damping forceand have a greater effect on overall compression damping forces. Inapplications where higher damping rates are required, such ashigh-leverage rear shock absorbers for motorcycles, the mid-valve shimstack is fixed securely to the piston face.

Rebound Adjusters

A rebound adjuster is a needle and orifice valve located at themid-valve. With exception to unique designs, fluid flows both directionthrough the valve, and therefore it affects compression damping as wellas rebound damping. However, the effect on rebound damping is much moresignificant than compression damping. This is because the rebound valveshim stack is attached securely to the piston face, not floating, so thevalve effectively seals off low-pressure fluid flow. Consequently, evena small fluid leak through the bypass can have a significant impact ondamping force. On the other hand, a mid-valve configured with float hasno ability to prevent low-pressure fluid flow, so the bypass orifice isinsignificant in comparison.

With current damper designs, the only effective way to adjust mid-valvecompression damping is to disassemble the damper and change themid-valve compression shim stack. Most people who use these products donot have the specialized knowledge and tools, not to mention the time,necessary to complete such a complex modification. While modernsuspension components offer effective and easy-to-access adjustmentcapabilities for all other damping circuits (rebound and base valvecompression), so far, none have an effective means of externallyadjusting mid-valve compression damping. Without the ability to adjustmid-valve compression, the end user's ability to tune suspension forvarying conditions or preferences is extremely limited.

The overall damping curve is highly sensitive to adjustments ofmid-valve stiffness. Vehicle manufacturers and suspension tuners choosethe shim setting carefully to yield the desired damping characteristics.

SUMMARY OF THE INVENTION

The present invention discloses an apparatus and method for externallyadjusting the mid-valve damping stiffness so that the end user is ableto tune his suspension system more effectively. The external adjustmentmechanisms disclosed here eliminate the need to disassemble the damperin order to adjust mid-valve stiffness. The effect of this adjustment onthe damping curve is larger than either low-speed compression adjustersor conventional high-speed compression adjusters. It combines thevalve-stiffening system of a high speed compression adjuster with thesensitivity of the mid-valve. In combination with a traditionallow-speed compression adjuster, the user has independent control of boththe slope and the vertical shift of the damping curve. Together, theseprovide near complete control of compression damping behavior withoutthe need for expert knowledge or time-consuming disassembly of thedamper.

As noted previously, the base valve is usually secured near the end of afork leg. This means the base valve is easier to access, requiressmaller and simpler parts, and has more space available in which toinstall concentric adjustment systems. The mid-valve is attached to theend of a long slender damping rod, remote from its connection to thestructural body of the damper. Accessing it is challenging. The problemis further complicated by the fact that the rebound adjuster mechanismresides at the same location. Adding an additional adjustment feature atthe mid-valve requires a series of long concentric rods that move insideone another and can adjust both mid-valve stiffness and rebound dampingindependently.

As detailed herein and as illustrated in the drawings, the adjustmentmechanism according to the invention may be beneficially used in bothclosed cartridge suspension forks (“CCSF”) and open cartridge suspensionforks (“OCSF”).

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawing, in which:

FIGS. 1 through 4 illustrate the external mid-valve adjustment systemaccording to the present invention as it is embodied in a “closedcartridge suspension fork” (“CCSF”), in which some of the components ofthe fork are shown to provide environment. Specifically:

FIG. 1 is a longitudinal cross sectional view of a CCSF showing thecomponents of the fork and the external mid-valve adjustment systemaccording to the present invention.

FIG. 2 is a cross sectional view of the “lower” end of the CCSF shown inFIG. 1, showing the external mid-valve adjustment system according tothe present invention.

FIG. 3 is a close up cross sectional view of the CCSF shown in FIG. 1and illustrating the mid-valve portion of the external mid-valveadjustment system according to the present invention.

FIG. 4 is a close up cross sectional view of the CCSF shown in FIG. 1and illustrating the adjuster portion of the external mid-valveadjustment system according to the present invention.

FIG. 5 is a cross sectional view of the mid-valve portion of themid-valve adjustment system according to the invention, in which themid-valve portion is shown in isolation without the cartridge tube. InFIG. 5 the pressure plate is in contact with and bearing on themid-valve shims.

FIG. 6 is a cross sectional view of the adjuster portion of themid-valve adjustment system according to the invention, in which theadjustment portion is shown in isolation without the fork lug or shocktube.

FIG. 7 is a perspective view of the adjuster portion of the mid-valveadjustment system illustrating the user-activated structures.

FIG. 8 is a cross sectional view of the mid-valve portion of themid-valve adjustment system according to the invention similar to theview of FIG. 5 except in FIG. 8 the pressure plate is spaced apart fromthe mid-valve shims.

FIG. 9 is an elevation view illustrating the mid-valve adjustmentmechanism of the present invention separated from the fork components.

FIGS. 10 and 11 are plots of performance data for a CCSF fork.Specifically:

FIG. 10 is a plot of the adjustment range for a CCSF fork including amid-valve adjustment mechanism according to the present invention.

FIG. 11 is a plot of the adjustment range for a CCSF fork that is fittedwith a conventional compression adjuster.

FIGS. 12 through 15 illustrate the external mid-valve adjustment systemaccording to the present invention as it is embodied in an “opencartridge suspension fork” (“OCSF”). Specifically:

FIG. 12 is a longitudinal cross sectional view of an OCSF showing thecomponents of the fork and the external mid-valve adjustment systemaccording to the present invention.

FIG. 13 is a cross sectional view of the “upper” end of the OCSF shownin FIG. 12, illustrating the external mid-valve adjustment systemaccording to the present invention.

FIG. 14 is a close up cross sectional view of the OCSF shown in FIG. 12and illustrating the mid-valve portion of the external mid-valveadjustment system according to the present invention.

FIG. 15 is a close up cross sectional view of the OCSF shown in FIG. 12and illustrating the adjuster portion of the external mid-valveadjustment system according to the present invention.

FIGS. 16 and 17 are plots of performance data for an OCSF fork.Specifically:

FIG. 16 is a plot of the adjustment range for an OCSF fork including amid-valve adjustment mechanism according to the present invention.

FIG. 17 is a plot of the adjustment range for an OCSF fork that isfitted with a conventional compression adjuster.

DETAILED DESCRIPTION OF PREFERRED AND ILLUSTRATED EMBODIMENTS

Relative directional terms are used at times in this description todescribe components of the invention and relative positions of theparts. As a naming convention, the ground plane is considered to be thegenerally horizontal surface on which a vehicle such as a motorcyclewith which the present invention is utilized may operate. Relativedirectional terms correspond to this convention: “upper” refers to thedirection above and away from the ground plane; “lower” is generally inthe opposite direction, “inward” is the direction from the exteriortoward the interior of the apparatus or a component thereof, “vertical”is the direction normal to the horizontal ground plane, and so on.

1. CCSF; Closed Cartridge Suspension Fork

With reference now to the drawings and specifically to FIGS. 1 through4, a closed cartridge suspension fork embodiment of the externalmid-valve adjustment system according to the present invention isillustrated along with typical components of one fork leg to describethe general environment in which the invention is used. In thisdescription, the external mid-valve adjustment system according to theinvention (also referred to in the shorthand as adjustment mechanism 10and at times, “revalve adjuster”) is identified generally with referencenumber 10. Adjustment mechanism 10 resides within fork 200, whichincludes an outer fork tube 202 and an inner fork tube 204 that isreciprocally slidable within the outer fork tube and which is sealedwith, for instance, a seal 206. In a CCSF the base valve assembly isretained in a cartridge tube 212 that is coaxially retained in outerfork tube 202 and fixed in the outer fork tube at the outer (i.e.,upper) end thereof, and which serves as a piston guide. The outer end ofthe outer fork tube is covered with a fork cap 210 and the fork capsecures the cartridge tube to the cap. On a vehicle such as amotorcycle, the outer fork tube 202 is positioned vertically above theinner fork tube 204, so utilizing the naming convention used in thisdescription the outer fork tube 202 is “above” the inner fork tube 204.The lowermost end of cartridge tube 212 extends into the inner fork tube204 as shown and includes a base 214 that has a bore 216.

The lower end of inner fork tube 204 comprises the fork lug 218 that isadapted to attach the fork 200 to the axle of a motorcycle (not shownbut conventional).

The adjustment mechanism 10 comprises an elongate assembly that has amid-valve assembly 12 at one end thereof, and a adjuster assembly 14 atthe opposite end. The mid-valve assembly and the adjuster assembly 14are interconnected with a damper rod 16, which as described belowcarries in its interior two separately rotatable rods that enable theuser to adjust the mid-valve and rebound performance. The damper rod 16effectively fixes the location of the mid-valve assembly 12 in the forktube. The adjuster assembly 14 is fixed in the inner tube 204 at forklug 218 and includes externally accessible adjustment mechanisms asdescribed in detail below that allow the user to independently adjustthe mid-valve and rebound performance. The mid-valve assembly 12 residesinternally in the cartridge tube 212—the damper rod 16 extends throughthe bore 216 in base 214.

The mid-valve assembly 12 is attached to the upper end of the dampingrod 16. The assembly 12 is not directly connected to any externalportion of the fork and cycles back and forth inside the cartridge tube212 as the suspension compresses and rebounds. The mid-valve assembly 12is a bi-directional valve: it generates damping force both when thedamper compresses and when it extends (compression force as the fork iscompressed, and rebound force as the fork extends). To accomplish this,as detailed below, the mid-valve assembly incorporates two sets of portsand two sets of shims oriented on opposite sides of a piston face.Unlike the base valve, fluid flow through the mid-valve assembly 12 doesnot depend on fluid displaced by the damping rod as it enters thecartridge. A larger volume of oil flows through the mid-valve assemblycompared to the base valve assembly, so other factors being equal, themid-valve assembly can generate more damping force than the base valve.

It will be appreciated that in use the outer fork tube 202 of fork 200is fixed to the motorcycle frame. The motorcycle wheel is mounted tofork lug 218 and as the wheel encounters uneven surfaces during movementthe inner fork tube 204 slides reciprocally into and out of outer forktube 202 (arrows A, FIG. 1). This reciprocal movement inner fork tube204 causes reciprocal movement of adjustment assembly 10, as detailedbelow.

The components just described are shown in greater detail in the viewsof FIGS. 2, 3 and 4. As indicated above, mid-valve assembly 12 resideswithin cartridge tube 212 interiorly of base 214 and such that damperrod 16 extends through bore 216 in the base 214, as shown best in FIGS.2 and 3. Damper rod 16 is fixedly attached to mid-valve assembly 12 andextends coaxially into a top out bumper 18, a rod cap 20; the interiorend of the damper rod abuts a shoulder 21 formed on adjacent rod cap 20.An adjustment spring 22 is located between a shoulder 24 on rod cap 20and applies outwardly directed pressure between the rod cap and apressure plate 25. The pressure plate 25 encircles a cylindrical portion27 of the rebound tap adjacent shoulder 24 and is movable on thecylindrical portion. The pressure plate 25 is normally urged away fromthe rod cap 20 as the adjustment spring 22 applies pressure betweenshoulder 24 and pressure plate 25. A valve body or piston 26 is attachedto a nipple or stem 28 that extends from rebound tap 19 and the outercircumference of the piston 26 is sealed to the interior circumferencesurface 30 of cartridge tube 212 with a wear ring or piston band 32. Itwill be thus appreciated that the cartridge tube functions as a guidefor the piston 26. A nut 34 is threaded onto the end of stem 28 tosecure the piston 26 to the rod cap with rebound shims 36 capturedtherebetween and held against the piston with the nut 34. The mid-valveshims 38 are retained against the opposite side of piston 26, facingpressure plate 25, and there are two fluid pathways through the piston,namely, the rebound circuit 40 and the compression circuit 42.Fluid—typically hydraulic fluid, flows through the rebound circuit 40and the compression circuit 42 as is known in the art and in thedirections of the arrows A and B in FIG. 3 in the respective rebound andcompression circuits 40 and 42.

A mid-valve adjustment rod 44 extends coaxially in the interior ofdamper rod 16 and is rotatable therein. A rebound adjustment rod 46extends coaxially in the interior of the mid-valve adjustment rod 44 andis separately rotatable therein. The “lower” ends of both the reboundadjustment rod 46 and the mid-valve adjustment rod 44—that is, the endof the rods toward the fork lug 218, extend through the fork lug so thatthey may be easily accessed and manipulated by a user. As detailedbelow, each of these adjustment rods 44 and 46 is separately rotatableby a user using conventional tools to adjust and tune the mid-valveassembly as desired.

The upper or interior end of the mid-valve adjustment rod 44 abuts ashoulder 80 formed on the rebound tap 19 and the rebound tap islongitudinally movable in the mid-valve assembly 12 when the mid-valveadjustment rod 44 is rotated by the user. Accordingly, as the mid-valveadjustment rod 44 moves longitudinally in response to a user rotatingthe rod the movement causes like longitudinal movement of the reboundtap and the components that are attached to and/or movable with therebound tap, namely, piston 26 and associated components.

The upper or interior end 45 of rebound adjustment rod 46 is threadedinto a rebound needle 70 at threaded portions 78 and 79 of theadjustment rod and the rebound needle, respectively. When the reboundadjustment rod 44 is manipulated (as detailed below) by a user rotatingthe rod, the rod is driven longitudinally and therefore the reboundneedle 70 is moved into and out of the mid-valve assembly 12. Morespecifically, rebound needle 70 moves longitudinally relative to anorifice 73 when the rebound adjustment rod 44 is rotated by virtue ofthe threaded engagement between threaded portion 78 of adjustment rod 44and a threaded interior 79 portion of the needle 70—FIG. 5.

This reciprocating movement caused by user-manipulation causes therebound needle 70 to move toward or away from the orifice 73 to adjustthe flow of fluid through the orifice at a bleed port 72.

Turning to FIGS. 4 and 6, as noted, the lower end of the adjustmentmechanism 10 defines the adjuster assembly 14 that is associated withfork lug 210. The fork lug assembly 218 is fixed to the inner fork tube204 and the adjuster assembly 14 extends through a bore 50 in fork lug210 that is coaxial with the inner fork tube 204. More specifically, thedamper rod 16, the rebound adjustment rod 46 and the mid-valveadjustment rod 44 are connected to the fork lug 210 with a threadedcoupler nut 52 in the interior of the inner fork tube 204; the damperrod 16 is not rotatable relative to the fork lug. The coupler nut 52 hasan outer facing end 54 that defines a threaded seat 56 that receives abase bolt 58. The exterior lip 60 of outer-facing end 54 abuts acircumferential shoulder 62 on fork lug 210 and a circumferential lip 64on base bolt 58 abuts the opposite side of shoulder 62 when the basebolt is threaded into the threaded seat 56 of the coupler nut, therebysecuring the adjuster assembly 14 to the fork lug. The base bolt 58 hasa threaded interior 66 and a mid-valve adjuster 68 is threaded into thethreaded interior 66.

The internal end of the mid-valve adjuster 68 is fixedly connected tothe mid-valve adjustment rod 44 and the exterior end 69 of the mid-valveadjuster 68 defines a user-accessible adjustment member; when themid-valve adjuster 68 is rotated by a user manipulating exterior end 69the opposite end of the mid-valve adjustment rod is driven into or outof (depending upon the direction of rotation of the adjuster) themid-valve assembly 12 as described above. The exterior end 69 maybeneficially be formed as a hexagonal member so that a standard wrenchmay be used to rotate the mid-valve adjustment rod 44 (see FIG. 7), andwritten indicia may be provided so that the user may adjust themechanism to a known setting.

A rebound adjuster 74 is connected coaxially into the interior of themid-valve adjuster 68 with a circlip (not shown) that allows the reboundadjuster 74 to rotate independently of the mid-valve adjuster 68. Therebound adjustment rod 46 is attached to the rebound adjuster 74 with asliding joint 77 that enables the adjuster 74 to transmit torque as theadjuster is rotated while allowing the rebound adjuster rod 46 to beable to move longitudinally (i.e., left and right in FIGS. 4 and 6) byvirtue of a threaded engagement on the adjustment needle 70 at theopposite (i.e., interior or upper) end of the adjustment rod 46 atthreaded portions 78 and 79. The exterior end 75 of the adjuster 74defines an exposed, user-accessible adjustment member; when the adjuster74 is rotated by a user the opposite end of the rebound adjustment rod46 is driven into or out of (depending upon the direction of rotation ofthe adjuster 74) the mid-valve assembly 12 as described above. Namely,rotation of the rebound adjustment rod 46 moves rebound needle 70 inrelation to orifice 73 to adjust the amount of fluid that may flowthrough the bleed port 72. The rebound adjuster 74 includes aconventional slot that may be engaged with a standard screw driver torotate the mid-valve adjustment rod. FIG. 7. A detent mechanism 76allows the user to control position of rotation of the exterior end 75incrementally as desired.

The mid-valve adjustment mechanism 12 described above and shown in thedrawings operatively connects external, user-accessible and visiblecomponents at the bottom of the fork lug with components inside the fork200 that mechanically increase or decrease compression damping generatedat the mid-valve assembly 12, thereby providing the user with theability to tune the damper/suspension component. Tuning the adjustmentmechanism 10 is a simple operation utilizing the present invention.Mid-valve adjustment assembly 12 is adjusted by rotating the mid-valveadjuster 68 (by the user manipulating the exterior end 69 of themid-valve adjuster) clockwise to thereby engage the threaded connectionbetween threaded interior 66, base bolt 58 and the mid-valve adjuster68; mid-valve adjuster 68 and mid-valve adjustment rod 44 are fixedtogether. This causes the mid-valve adjustment rod 44 to thread outwardaway from the adjuster body (left-hand threads are used). Severalcomponents are semi-permanently connected to the mid-valve assembly 12:mid-valve adjustment rod 44, rebound tap 19, valve piston 26 and reboundshims 36 and mid-valve shims 38, and nut 34. As this group of componentsmoves downward relative to the rest of the fork as the mid-valveadjuster 68 is rotated by the user, the mid-valve shims 38 are broughtinto contact with pressure plate 25. This position is shown in the crosssectional view of FIG. 5. Stated another way, in FIG. 5 the mid-valveadjustment assembly 12 is in the closed position and the adjustmentspring 22 is under tension. In this position the pressure plate 25exerts pressure on the mid-valve shims 38. The rebound needle 70 isillustrated in the closed position so that the bleed port 72 is closed.The rebound needle 70 stays in the same position relative to the bleedport orifice 73 as the mid-valve is adjusted. The farther the adjusteris rotated, the more adjustment spring 22 is compressed and the greaterpressure it exerts against the stack of shims defining mid-valve shims38, thereby stiffening the assembly and its operating characteristics.It will further be noted that in FIG. 5 the rebound adjustment rod 46 isin a position such that the rebound needle 70 is adjusted so that thebleed port 72 is closed. This is in contrast to the position of therebound needle 70 illustrated in FIG. 3 where the rebound adjustment rodhas been adjusted so that the rebound needle 70 is withdrawn so that thebleed port 72 is open.

The example shown in the drawings utilizes a clamped shim design inmid-valve assembly 12, meaning that there is no float. In the full softposition, the pressure plate 25 does not contact the mid-valve shims 38,so that the shims can bend freely without any influence from thepressure plate. When the adjuster is tightened a small amount, thepressure plate 25 moves closer to the shims 38, so that the plate 25contacts the shims when the shims 38 flex away from the adjacent face ofvalve piston 26 during a compression event. This stiffens the valveduring suspension movements that flex the shims far enough to contactthe pressure plate.

As the mid-valve adjuster 68 is tightened further, the pressure plate 55comes into the contact with the shims 38 while they are in the flat andunstressed, non-flexed position. In this position it becomes necessaryto deflect both the shims 38 and the pressure plate 25 in order to openthe valve, making the valve stiffer yet. At tighter adjustment settings,the adjustment spring 22 becomes preloaded, increasing both the initialvalve opening force and the force required to further deflect the shims.This adjustment scheme is highly effective, and covers a wide range ofsettings useful to the rider.

The exact design of the mid-valve pressure plate, shim stackconfiguration, stiffness and size of the mid-valve adjustment spring allaffect the function of the adjuster. In practice, these components areall fine-tuned to deliver the desired damping characteristics atdifferent stiffness settings.

Turning to FIG. 8, the mid-valve assembly 12 has been adjusted to anopen position in which the pressure plate 25 is spaced apart from themid-valve shims 38. In this position the adjustment spring 22 isneutral, neither under compression nor tension. The adjustment spring iscompressed when the mid-valve assembly 12 is drawing downwardly, puttingtension on the spring that is transmitted to the mid-valve shims 38. Andin FIG. 8 the rebound adjustment rod 44 has been adjusted so that therebound needle 70 is spaced apart from orifice 73 so that bleed port 72is open.

Use of the spring and pressure plate mechanism as described above thusallows adjustment of damping in a mid-valve. Moreover, in the mid-valveadjustment mechanism described herein the rebound needle is used toadjust rebound damping instead of low-speed compression damping.

The rebound adjuster assembly 14 operates independently of the mid-valveadjustment assembly 12 but it will be appreciated that the entirerebound adjustment assembly 14 moves simultaneously and in tandem withthe mid-valve adjustment assembly 12 when it is adjusted as describedabove, so regardless of what setting is used for the mid-valveadjustment, rebound damping performance remains consistent. The reverseis also true: adjustment of the rebound adjustment assembly 14 has noeffect on the mid-valve adjustment system. Said another way, adjustmentof the mid-valve adjustment assembly 12 to causes movement of piston 26results in simultaneous movement of the rebound needle 70 but theposition of the rebound needle relative to the orifice 73 is notchanged, and vice versa.

Various performance data for a damper in which a mid-valve adjustmentmechanism 10 according to the invention has been installed in a CCSFfork are presented in graphic form in the series of FIGS. 10 and 11. InFIG. 10 the suspension comprises a CCSF fork that utilizes a mid-valveadjustment mechanism 10 according to the present invention andillustrates the adjustment range. In contrast, the graph in FIG. 11illustrates a CCSF fork that incorporates a conventional compressionadjuster. The performance increases provided by the mid-valve adjustmentmechanism 10 according to the present invention are clearly shown in theperformance data.

2. OCSF; Open Cartridge Suspension Fork

As noted previously, the revalve adjustment mechanism 10 works similarlyin an OCSF to the embodiment of FIGS. 1 through 9, but in an OCSF themechanism is inverted and the valve stiffening mechanism uses mid-valvefloat adjustment instead of a pressure plate to adjust damping. An OCSFtype of fork requires lower mid-valve forces due to its valve andcartridge dimensions, and the unpressurized design. Normal shimconfigurations used with an OCSF design usually include float values inthe range of 0.2 to 1.5 mm. This embodiment of the invention isillustrated specifically in FIGS. 12 through 15 and the same referencenumbers are used throughout the specification to identify likecomponents.

The relative inversion of the components in an OCSF fork compared to aCCSF fork is best seen with reference to FIG. 12. The fork 200 has anouter tube 202 and inner tube 204, but the base valve assembly 208 isfixedly located at the bottom of the inner tube 204, adjacent the forklug 218. A cartridge tube 212 is carried in the inner tube 204 as shownwith the lower end of the cartridge tube fixed to the fork lug 218,which serves as a cap to secure the cartridge tube in the inner tube204. The mid-valve adjustment mechanism 12 is carried in the cartridgetube 212 with the mid-valve assembly 12 oriented oppositely of the samestructure in the CCSF fork, and the adjuster assembly 14 positioned atthe top of the fork and accessible through the fork cap 210 rather thanthrough the fork lug 218 as with the CCSF fork. The damper rod 16includes an externally accessible adjuster, detailed below, which isaccessed by the user through the fork cap 210. The mid-valve assembly 12shown in the OCSF fork herein does not include the rebound adjustmentcomponents as the rebound adjustment is not required in the illustratedembodiment of the fork. It may be noted nonetheless that a reboundadjuster may be necessary and used in different OCSF designs and thesame mechanisms described above and as shown in FIGS. 1 through 9 may beused with an OCSF fork such as that shown in FIGS. 12 through 15.

The mid-valve adjustment rod 44 is concentrically and rotatably retainedin damper tube 16 in the same manner as described above and is coupledto the mid-valve assembly 12 with a mid-valve coupler 90; the damper rodabuts a shoulder on the mid-valve base 93. The mid-valve assembly 12used with the OCSF fork does not include a pressure plate 25. Instead, acheck spring 23 is captured between the mid-valve shims 38 and themid-valve base 93. As the mid-valve assembly 12 is adjusted, the floatadjustment star 92 moves relative to the piston 26, contracting orexpanding the distance the mid-valve shims 38 are able to displacefreely away from the piston 26 during a compression stroke. On the OCSFfork shown in FIGS. 12 through 15, the check spring 23 does not applyany significant pressure to the shims regardless of the adjustmentsetting. Instead, the check spring 23 only serves to close the float gapand close the valve when a compression stroke ends and a rebound strokebegins. The shims have to cover the compression ports during reboundflow.

The adjuster assembly 12 is shown in FIG. 15 and as noted above, is partof the fork cap 210 and is accessible at the top of the fork 200 whenthe OCSF fork is mounted on a motorcycle. The damper rod 16 terminatesin a seat 96 formed in the fork cap 210 and abuts a shoulder 98. Themid-valve adjustment rod 44 extends further into the fork cap 210 asshown and connects to a mid-valve adjustment screw 94 that is threadedinto a bore 100 in cap 210. The screw 94 defines the user-manipulatedcomponent that the user rotates to adjust the mid-valve assembly 12 andto thereby tune the mechanism—as noted, the adjustment screw 94 iscoupled to the mid-valve rod 44.

When mid-valve adjustment screw 94 is rotated clockwise, the threadedconnection between the screw 94 and fork cap 210 causes the screw tomove inwardly relative to the fork cap and all external parts connectedto it move in the same direction. As the mid-valve adjustment rod 44 istranslated longitudinally the end of the rod presses against themid-valve coupler 90 and adjustment star 92. The adjustment star 92 setsthe float limit, in other words, the distance mid-valve shims 38 mayfreely displace away from the piston 26 before encountering a hard stop.During a compression event, first the float value is maximized as fluidbegins to flow through the valve. As pressure and flow volume increases,the shims begin to restrict flow and generate damping. Large floatvalues create less restriction and less damping; less or no floatcreates more damping.

Rebound tap 19 has a collar 102 that piston 26 rests upon. The insidediameter of the bore through the mid-valve shims 28 is larger than theouter diameter of the collar 102 so the shims 38 can move freely up anddown the rebound tap 19 (i.e., “float”). Check spring 23 closes thevalve upon backflow (rebound), in order to channel fluid into therebound ports during fork extension. The check spring 23 is designed tohelp close the valve during rebound, but is not stiff enough to providesignificant resistance to flow in the compression direction. The shimconfiguration and float value determined by the position of the floatadjustment star are the main factors influencing the amount ofcompression damping generated by the valve.

Referring now to FIGS. 16 and 17, plots of data for an OCSF fork areshown. In FIG. 16 the adjustment range data from an OCSF fork comprisingthe revalve adjustment mechanism 10 according to the invention areshown. Contrasting with FIG. 16, in FIG. 17 the adjustment range datafrom an OCSF fork utilizing a conventional suspension system are shown(i.e., “OEM”).

Those of ordinary skill in the art will recognize that certainmodifications may be made to the apparatus and methods described aboveto achieve equivalent functionality, without departing from the scope ofthe inventions described herein. As an example of such equivalency, thestructures described above that enable a user to access the mid-valveadjustment rod externally and rotate the rod to cause longitudinalmovement of the rod and associated adjustment of the damping force maybe replaced by other structures that cause the rod to movelongitudinally. Thus, a threaded mechanism that causes longitudinalmovement of the rod may be replace by another mechanism that causeslongitudinal movement of the mid-valve adjustment rod, such as a cam ora ratcheted drive. A hydraulically-actuated drive mechanism or a drivemechanism using an electric motor could also be used to drivelongitudinal movement of the mid-valve adjustment rod to achieve thesame functionality.

While the present invention has been described in terms of preferred andillustrated embodiments, it will be appreciated by those of ordinaryskill that the spirit and scope of the invention is not limited to thoseembodiments, but extend to the various modifications and equivalents asdefined in the appended claims.

The invention claimed is:
 1. An apparatus for adjusting damping forcecreated by a bi-directional mid-valve assembly in a suspension system,comprising: a bi-directional mid-valve assembly operable to createcompression damping force with a mid-valve compression damping componenton a first side of a piston, and rebound damping force with a rebounddamping component on a second side of the piston; an elongate dampingrod having a first end coupled to the bi-directional mid-valve assemblyand a second end; a mid-valve compression damping component adjustmentrod received in and longitudinally movable in the elongate damping rod,the mid-valve compression damping component adjustment rod having afirst end interacting with the mid-valve compression damping componentand a second end; a user-accessible first actuator having a first end incontact with the second end of the mid-valve compression dampingcomponent adjustment rod, and a second end; wherein the mid-valvecompression damping component is adjusted by manipulating the firstactuator to thereby cause longitudinal movement of the mid-valvecompression damping component adjustment rod to thereby adjust thecompression damping force created by the bi-directional mid-valveassembly; a rebound adjustment rod received in and longitudinallymovable in the mid-valve compression damping component adjustment rod,the rebound adjustment rod having a first end interacting with a bleedorifice in the bi-directional mid-valve assembly, and a second end; auser-accessible second actuator having a first end in contact with thesecond end of the rebound adjustment rod, and a second end; wherein themid-valve compression damping component adjustment rod is coaxiallyreceived in the elongate damping rod and the first actuator isconcentric with the mid-valve compression damping component adjustmentrod.
 2. The apparatus according to claim 1 in which rotation of themid-valve compression damping component adjustment rod in a firstrotational direction causes the first end of the mid-valve compressiondamping component adjustment rod to move longitudinally in a firstdirection and rotation of the mid-valve compression damping componentadjustment rod in a second rotational direction causes the first end ofthe mid-valve adjustment compression damping component rod to movelongitudinally in a second direction that is opposite the firstdirection.
 3. The apparatus according to claim 2 in which the reboundadjustment rod is rotatably received in the mid-valve compressiondamping component adjustment rod and longitudinally movable therein, andthe user-accessible second actuator is concentric with the reboundadjustment rod and the mid-valve compression damping componentadjustment rod.
 4. The apparatus according to claim 3 in which rotationof the rebound adjustment rod in a first rotational direction causes therebound adjustment rod to move longitudinally in a first direction androtation of the rebound adjustment rod in a second rotational directioncauses the rebound adjustment rod to move longitudinally in a seconddirection that is opposite of the first direction.
 5. The apparatusaccording to claim 4 in which rotation of the user-accessible secondactuator in a first rotational direction causes rebound adjustment rodto move longitudinally in a first direction and rotation of theuser-accessible second actuator in a second rotational direction causesthe rebound adjustment rod to move longitudinally independently of themid-valve compression damping component adjustment rod.
 6. The apparatusaccording to claim 5 wherein the first end of the rebound adjustment roddefines a rebound needle that moves toward the bleed orifice in thebi-directional mid-valve assembly when the rebound adjustment rod isrotated in the first rotational direction and the rebound needle movesaway from the bleed orifice when the rebound adjustment rod is rotatedin the second rotational direction.
 7. The apparatus according to claim6 in which the piston, rebound needle and bleed orifice arelongitudinally movable together by rotation of the mid-valve compressiondamping component adjustment rod.
 8. The apparatus according to claim 7wherein longitudinal movement of the rebound needle by rotation of therebound adjustment rod is independent of longitudinal movement of thepiston.
 9. The apparatus according to claim 7 further comprising: a forktube defined by an outer fork tube and an inner fork tube that isreciprocally slidable in the outer fork tube, each of the outer andinner fork tubes having first and second opposite ends and each of theouter and inner fork tubes having a cap attached to one of the first orsecond opposite ends; a cartridge tube received in a selected one of theinner or outer fork tube; wherein the bi-directional mid-valve assemblyis received in the cartridge tube, the second end of the elongatedamping rod is connected to a first one of the caps, the second end ofthe user-accessible first actuator is accessible through an exterior ofthe first one of the caps, and the second end of the user-accessiblesecond actuator is accessible through the exterior of the first one ofthe caps.
 10. The apparatus according to claim 9 in which the first oneof the caps is defined by a fork lug.
 11. The apparatus according toclaim 9 in which the first one of the caps is a fork tube cap.
 12. Theapparatus according to claim 11 in which the mid-valve adjustment rod isaccessible through a bore in the fork tube cap.
 13. A method ofadjusting a bi-directional mid-valve assembly in a suspension systemhaving a fork, the fork having an upper end and a lower end and the forkdefined by an outer fork tube having an upper and lower end and an innerfork tube having an upper and lower end, the upper end and the lower endof the fork each having an end cap, and a cartridge tube within theinner fork tube and attached to a selected one of the end caps,comprising the steps of: a. forming a bore through a selected one of theend caps; b. locating a bi-directional mid-valve assembly in the fork inthe cartridge tube; c. extending a damping rod from the bi-directionalmid-valve assembly to the end cap opposite of the end cap to which thecartridge tube is attached; d. inserting a bi-directional mid-valveassembly compression damping adjustment rod coaxially and rotatably intothe damping rod so that a first end of the mid-valve assemblycompression damping adjustment rod interacts with a compression dampingcomponent and so that a second end of the mid-valve assembly compressionadjustment rod is accessible externally of the selected one of the endcaps; e. longitudinally moving the mid-valve assembly compressiondamping adjustment rod to thereby adjust the compression damping of themid-valve assembly.
 14. The method according to claim 13 including thestep of inserting a rebound damping component adjustment rod coaxiallyand rotatably into the mid-valve assembly compression damping adjustmentrod so that a rebound needle at a first end of the rebound dampingcomponent adjustment rod interacts with an orifice in the bi-directionalmid-valve assembly and so that a second end of the rebound dampingcomponent adjustment rod is accessible externally of the selected one ofthe end caps, and in which the step of manipulating the mid-valveassembly compression damping adjustment rod further comprises accessingthe second end of the mid-valve assembly compression damping adjustmentrod externally of the selected one of the end caps.
 15. The methodaccording to claim 14 wherein the step of rotating the mid-valveassembly compression damping adjustment rod moves the bi-directionalmid-valve assembly relative to the damping rod and causes movement ofthe rebound needle and orifice simultaneously with movement of thepiston but does not change the position of the rebound needle relativeto the orifice.
 16. An adjustment apparatus for a suspension system,comprising: a fork having an outer fork tube and an inner fork tube thatis reciprocally slidable in the outer fork tube, each of the outer andinner fork tubes having opposite ends and a cap attached to one of theopposite ends of each of the outer and inner fork tubes; a cartridgetube in the fork, the cartridge tube having opposite first and secondends with one of either the first or second ends attached to the cap ofone of either the outer or inner fork tubes and the opposite end of thecartridge tube not fixed; a bi-directional mid-valve assembly in thecartridge tube, the bi-directional mid-valve assembly coupled by adamping rod to the cap of the one of either the outer fork tube or theinner fork tube to which the cartridge tube is not fixed; abi-directional mid-valve assembly compression damping adjustment rodreceived and movable in the damper rod, the bi-directional mid-valveassembly compression damping adjustment rod operable to adjustbi-directional mid-valve assembly compression damping and having a firstend coupled to the bi-directional mid valve assembly and a second end incontact with a bi-directional mid-valve assembly compression dampingadjuster that is accessible at the cap of the one of either the outerfork tube or the inner fork tube to which the cartridge tube is notfixed so that manipulation of the bi-directional mid-valve assemblycompression damping adjuster causes movement of the bi-directionalmid-valve assembly compression damping adjustment rod.
 17. Theadjustment apparatus according to claim 16 in which the cap of the oneof either the outer fork tube or the inner fork tube is defined by afork lug fixed to a lower end of the inner fork tube.
 18. The adjustmentapparatus according to claim 16 in which the cap of the one of eitherthe outer fork tube or the inner fork tube is defined by a fork capfixed to an upper end of the outer fork tube.
 19. The adjustmentapparatus according to claim 16 further comprising a bi-directionalmid-valve assembly rebound damping adjustment rod coaxially androtatably received in the bi-directional mid-valve assembly compressiondamping adjustment rod, the bi-directional mid-valve assembly rebounddamping adjustment rod having a first end defining a rebound needle inthe bi-directional mid-valve assembly and a second end defining arebound damping adjuster that is accessible at the cap of the one ofeither the outer fork tube or the inner fork tube to which the cartridgetube is not fixed so that manipulation of the rebound damping adjustercauses movement of the bi-directional mid-valve assemble rebound dampingadjustment rod, and wherein the bi-directional mid-valve assemblycompression damping adjustment rod and bi-directional mid-valve assemblerebound damping adjustment rod are concentric to one another.
 20. In asuspension system having a bi-directional mid-valve assembly designed tocreate compression and rebound damping, the improvement comprising: abi-directional mid-valve assembly comprising a piston, compressiondamping adjustment components on a first side of the piston and rebounddamping adjustment components on a second side of the piston, the pistoncoupled to and longitudinally movable relative to a damping rod; anexternally accessible compression damping adjuster coupled to thecompression damping components by a first rod coaxially and rotatablyreceived in the damping rod so that rotation of the compression dampingadjuster in a first direction increases the compression damping of thebi-directional mid-valve assembly and rotation of the compressiondamping adjuster in a second direction decreases compression damping ofthe bi-directional mid-valve assembly; an externally accessible rebounddamping adjuster coupled to the rebound damping components by a secondrod coaxially and rotatably received in the first rod so that rotationof the rebound damping adjuster in a first direction increases therebound damping of the bi-directional mid-valve assembly and rotation ofthe rebound damping adjuster in a second direction decreases rebounddamping of the bi-directional mid-valve assembly; and wherein the pistonis longitudinally movable relative to the damping rod.
 21. Theimprovement according to claim 20 in which the suspension system is aclosed cartridge suspension system.
 22. The improvement according toclaim 20 in which the suspension system is an open cartridge suspensionsystem.
 23. The improvement according to claim 20 in which the damperrod locates the bi-directional mid-valve assembly in a fork tube and theexternally accessible compression damping is externally accessiblethrough a fork lug at a lower end of the fork tube.
 24. The improvementaccording to claim 20 in which the damper rod locates the bi-directionalmid-valve assembly in a cartridge tube and the externally accessiblecompression damping is externally accessible through a fork cap at anupper end of the fork.